The broad objectives of this project fall into two categories. First, the mechanism of action of cardiac glycosides is under investigation by the use of biochemical techniques to localize the cellular receptor site. Further experiments are planned to attempt to purify and further characterize myocardial Na ion, K ion - ATPase. The second major objective is the purification and characterization of cardiac glycoside-specific antibodies for possible therapeutic use in cases of life-threatening digitalis intoxication. A purification technique has been developed using a ouabain-ribonuclease-bromoacetyl cellulose immunoadsorbent, and highly purified digoxin-specific gamma globulin and Fab fragments being studied for ability to reverse established digoxin intoxication in canine experimental models. Further studies are underway to evaluate the antigenicity of purified gamma globulin and Fab fragments in animals, in order to gain further insight into the potential risks associated with therapeutic use of purified digoxin-specific antibodies or Fab fragments.